Explicitly only support 65-byte length sigs (#13)

Author: mdehoog

src/Paymaster.sol

@@ -68,9 +68,8 @@ contract Paymaster is BasePaymaster {
     function _validatePaymasterUserOp(UserOperation calldata userOp, bytes32 /*userOpHash*/, uint256 /*requiredPreFund*/)
     internal view override returns (bytes memory context, uint256 validationData) {
         (uint48 validUntil, uint48 validAfter, bytes calldata signature) = parsePaymasterAndData(userOp.paymasterAndData);
-        // ECDSA library supports both 64 and 65-byte long signatures.
-        // we only "require" it here so that the revert reason on invalid signature will be of "Paymaster", and not "ECDSA"
-        require(signature.length == 64 || signature.length == 65, "Paymaster: invalid signature length in paymasterAndData");
+        // Only support 65-byte signatures, to avoid potential replay attacks.
+        require(signature.length == 65, "Paymaster: invalid signature length in paymasterAndData");
         bytes32 hash = ECDSA.toEthSignedMessageHash(getHash(userOp, validUntil, validAfter));
 
         // don't revert on signature failure: return SIG_VALIDATION_FAILED

test/Paymaster.t.sol

@@ -64,7 +64,7 @@ contract PaymasterTest is Test {
         UserOperation memory userOp = createUserOp();
         signUserOp(userOp);
 
-        vm.expectRevert(createEncodedValidationResult(false, 57126));
+        vm.expectRevert(createEncodedValidationResult(false, 57098));
         entrypoint.simulateValidation(userOp);
     }
 
@@ -76,7 +76,7 @@ contract PaymasterTest is Test {
         userOp.paymasterAndData = abi.encodePacked(address(paymaster), abi.encode(MOCK_VALID_UNTIL, MOCK_VALID_AFTER), r, s, v);
         signUserOp(userOp);
 
-        vm.expectRevert(createEncodedValidationResult(false, 55126));
+        vm.expectRevert(createEncodedValidationResult(false, 55098));
         entrypoint.simulateValidation(userOp);
     }
 
@@ -86,7 +86,7 @@ contract PaymasterTest is Test {
         userOp.paymasterAndData = abi.encodePacked(address(paymaster), abi.encode(MOCK_VALID_UNTIL, MOCK_VALID_AFTER), r, s, v);
         signUserOp(userOp);
 
-        vm.expectRevert(createEncodedValidationResult(true, 57132));
+        vm.expectRevert(createEncodedValidationResult(true, 57104));
         entrypoint.simulateValidation(userOp);
     }